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Item Unification of quantum Zeno–anti Zeno effects and parity-time symmetry breaking transitions(APS, 2023) Li, Jiaming; Wang, Tishuo; Luo, Le; Vemuri, Sreya; Joglekar, Yogesh N.; Physics, School of ScienceThe decay of an unstable quantum state can be inhibited or enhanced by tailored measurements, known as quantum Zeno effect (QZE) or anti Zeno effect (QAZE). QZE(QAZE) has been intensively explored in terms of the cases of various system-environment couplings, where the time evolution can be affected either by the projective measurements, or through the dissipative couplings to the environment. A general relation between QZE(QAZE) and the dissipation, for arbitrary dissipation strength and periodicity, is yet to be developed. In this paper, we show a framework to unify the QZE(QAZE) and the parity-time (𝒫𝒯) symmetry breaking transition, where the pure dissipative Hamiltonian is mapped onto a 𝒫𝒯 symmetric non-Hermitian Hamiltonian. This method uses the 𝒫𝒯 symmetry transitions to distinguish QZE and QAZE, and can be applied to analyze the crossover behavior between these two effects. Using a heuristic example of a two-level system which is coupled to environment by periodical dissipation, we show the relation diagram between the QZE(QAZE) and the 𝒫𝒯 symmetry breaking transition, in which the QZE appears at an exceptional point that separates the 𝒫𝒯 symmetric (PTS) phase and the 𝒫𝒯 symmetry broken (PTSB) phase, and ends at the resonance point of the maximum 𝒫𝒯 symmetry breaking; after that, QAZE exists at the rest of the PTSB phase and remains in the next PTS phase. This interesting finding reveals a hidden relation between the QZE–QAZE and PTS-PTSB phases in a non-Hermitian quantum system.Item Suppression of spin pumping at metal interfaces(AIP, 2023-10) Lim, Youngmin; Nepal, Bhuwan; Smith, David A.; Wu, Shuang; Srivastava, Abhishek; Nakarmi, Prabandha; Mewes, Claudia; Jiang, Zijian; Gupta, Adbhut; Viehland, Dwight D.; Klewe, Christoph; Shafer, Padraic; Park, In Jun; Mabe, Timothy; Amin, Vivek P.; Heremans, Jean J.; Mewes, Tim; Emori, Satoru; Physics, School of ScienceAn electrically conductive metal typically transmits or absorbs a spin current. Here, we report on evidence that interfacing two metal thin films can suppress spin transmission and absorption. We examine spin pumping in spin-source/spacer/spin-sink heterostructures, where the spacer consists of metallic Cu and Cr thin films. The Cu/Cr spacer largely suppresses spin pumping—i.e., neither transmitting nor absorbing a significant amount of spin current—even though Cu or Cr alone transmits a sizable spin current. The antiferromagnetism of Cr is not essential for the suppression of spin pumping, as we observe similar suppression with Cu/V spacers with V as a nonmagnetic analog of Cr. We speculate that diverse combinations of spin-transparent metals may form interfaces that suppress spin pumping, although the underlying mechanism remains unclear. Our work may stimulate a new perspective on spin transport in metallic multilayers.Item Study of the Long-Range Exchange Coupling in Nd-Fe-B/Ti/Fe Multilayered Structure(MDPI, 2024-02) Yazdani, Saeed; Phillips, Jared; Mosey, Aaron; Bsaibes, Thomas; Decca, Ricardo; Cheng, Ruihua; Physics, School of ScienceThe exchange coupling between two ferromagnetic thin films, one with magnetically hard and the other with soft phases, separated by a thin non-magnetic layer, is studied. Nd-Fe-B/Ti/Fe thin film heterostructures were fabricated using DC magnetron sputtering on Si substrates, which were heated in situ at 650 °C using a house-built vacuum-compatible heater. The effect of the thickness of the Ti buffer layer and the annealing temperature on the formation of various phases of Nd-Fe-B was investigated. The effect of the thickness of the non-magnetic Ti spacer layer on the exchange coupling strength between the hard phase Nd-Fe-B ferromagnetic thin layer and the soft phase transition metal Fe layer was experimentally investigated. Hysteresis loops of multilayer thin films indicate an antiferromagnetic coupling was observed when the thickness of the spacer layer was 2 nm. This is within the range of an antiferromagnetic coupling calculation based on RKKY theory predictions.Item Endoglucanases: insights into thermostability for biofuel applications(Springer Nature, 2013-09-27) Yennamalli, Ragothaman M.; Rader, Andrew J.; Kenny, Adam J.; Wolt, Jeffrey D.; Sen, Taner Z.; Physics, School of ScienceObtaining bioethanol from cellulosic biomass involves numerous steps, among which the enzymatic conversion of the polymer to individual sugar units has been a main focus of the biotechnology industry. Among the cellulases that break down the polymeric cellulose are endoglucanases that act synergistically for subsequent hydrolytic reactions. The endoglucanases that have garnered relatively more attention are those that can withstand high temperatures, i.e., are thermostable. Although our understanding of thermostability in endoglucanases is incomplete, some molecular features that are responsible for increased thermostability have been recently identified. This review focuses on the investigations of endoglucanases and their implications for biofuel applications.Item Strong Casimir force reduction through metallic surface nanostructuring(Springer Nature, 2013) Intravaia, Francesco; Koev, Stephan; Jung, Il Woong; Talin, A. Alec; Davids, Paul S.; Decca, Ricardo S.; Aksyuk, Vladimir A.; Dalvit, Diego A. R.; López, Daniel; Physics, School of ScienceThe Casimir force between bodies in vacuum can be understood as arising from their interaction with an infinite number of fluctuating electromagnetic quantum vacuum modes, resulting in a complex dependence on the shape and material of the interacting objects. Becoming dominant at small separations, the force has a significant role in nanomechanics and object manipulation at the nanoscale, leading to a considerable interest in identifying structures where the Casimir interaction behaves significantly different from the well-known attractive force between parallel plates. Here we experimentally demonstrate that by nanostructuring one of the interacting metal surfaces at scales below the plasma wavelength, an unexpected regime in the Casimir force can be observed. Replacing a flat surface with a deep metallic lamellar grating with sub-100 nm features strongly suppresses the Casimir force and for large inter-surfaces separations reduces it beyond what would be expected by any existing theoretical prediction.Item Quantum metrology with parametric amplifier-based photon correlation interferometers(Springer Nature, 2014) Hudelist, F.; Kong, Jia.; Liu, Cunjin; Jing, Jietai; Ou, Z. Y.; Zhang, Weiping; Physics, School of ScienceConventional interferometers usually utilize beam splitters for wave splitting and recombination. These interferometers are widely used for precision measurement. Their sensitivity for phase measurement is limited by the shot noise, which can be suppressed with squeezed states of light. Here we study a new type of interferometer in which the beam splitting and recombination elements are parametric amplifiers. We observe an improvement of 4.1±0.3 dB in signal-to-noise ratio compared with a conventional interferometer under the same operating condition, which is a 1.6-fold enhancement in rms phase measurement sensitivity beyond the shot noise limit. The improvement is due to signal enhancement. Combined with the squeezed state technique for shot noise suppression, this interferometer promises further improvement in sensitivity. Furthermore, because nonlinear processes are involved in this interferometer, we can couple a variety of different waves and form new types of hybrid interferometers, opening a door for many applications in metrology.Item Self-induced inverse spin Hall effect in La0.67Sr0.33MnO3 films(APS, 2024-01) Gupta, Pushpendra; Park, In Jun; Swain, Anupama; Mishra, Abhisek; Amin, Vivek P.; Bedanta, Subhankar; Physics, School of ScienceThe efficient generation of spin currents and spin torques via spin-orbit coupling is an important goal of spintronics research. One crucial metric for spin current generation is the spin Hall angle, which is the ratio of the spin Hall current to the transversely flowing charge current. A typical approach to measure the spin Hall angle in nonmagnetic materials is to generate spin currents via spin pumping in an adjacent ferromagnetic layer and measure the transverse voltage from the inverse spin Hall effect in the nonmagnetic layer. However, given that the spin Hall effect also occurs in ferromagnets, single ferromagnetic layers could generate a self-induced transverse voltage during spin pumping as well. Here we show that manganite-based La0.67Sr0.33MnO3 (LSMO) films deposited by pulsed laser deposition exhibit a significant self-induced inverse spin Hall voltage while undergoing spin pumping. A spin pumping voltage of 1.86µV is observed in the LSMO (12 nm) film. Using density functional theory and the Kubo formalism, we calculate the intrinsic spin current conductivities of these films and show that they are in reasonable agreement with the experimental measurements.Item Stability of 𝒫𝒯 and anti-𝒫𝒯-symmetric Hamiltonians with multiple harmonics(APS, 2024) Cen, Julia; Joglekar, Yogesh N.; Saxena, Avadh; Physics, School of ScienceHermitian Hamiltonians with time-periodic coefficients can be analyzed via Floquet theory, and have been extensively used for engineering Floquet Hamiltonians in standard quantum simulators. Generalized to non-Hermitian Hamiltonians, time periodicity offers avenues to engineer the landscape of Floquet quasienergies across the complex plane. We investigate two-level non-Hermitian 𝒫𝒯 and anti-𝒫𝒯-symmetric Hamiltonians with coefficients that have multiple harmonics using Floquet theory. By analytical and numerical calculations, we obtain their regions of stability, defined by real Floquet quasienergies, and contours of exceptional point (EP) degeneracies. We extend our analysis to study the phases that accompany these cyclic changes with the biorthogonality approach. Our results demonstrate that these time-periodic Hamiltonians generate a rich landscape of stable (real) and unstable (complex) regions.Item Search for Ultraheavy Dark Matter from Observations of Dwarf Spheroidal Galaxies with VERITAS(IOP, 2023-03) Acharyya, A.; Archer, A.; Bangale, P.; Bartkoske, J. T.; Batista, P.; Baumgart, M.; Benbow, W.; Buckley, J. H.; Falcone, A.; Feng, Q.; Finley, J. P.; Foote, G. M.; Fortson, L.; Furniss, A.; Gallagher, G.; Hanlon, W. F.; Hervet, O.; Hoang, J.; Holder, J.; Humensky, T. B.; Jin, W.; Kaaret, P.; Kertzman, M.; Kherlakian, M.; Kieda, D.; O'Brien, S.; Ong, R. A.; Pfrang, K.; Pohl, M.; Pueschel, E.; Quinn, J.; Ragan, K.; Reynolds, P. T.; Roache, E.; Rodd, N. L.; Ryan, J. L.; Sadeh, I.; Saha, L.; Santander, M.; Sembroski, G. H.; Shang, R.; Splettstoesser, M.; Tak, D.; Tucci, J. V.; Vassiliev, V. V.; Williams, D. A.; Physics, School of ScienceDark matter is a key piece of the current cosmological scenario, with weakly interacting massive particles (WIMPs) a leading dark matter candidate. WIMPs have not been detected in their conventional parameter space (100 GeV ≲Mχ ≲ 100 TeV), a mass range accessible with current Imaging Atmospheric Cherenkov Telescopes. As ultraheavy dark matter (UHDM; Mχ ≳ 100 TeV) has been suggested as an underexplored alternative to the WIMP paradigm, we search for an indirect dark matter annihilation signal in a higher mass range (up to 30 PeV) with the VERITAS γ-ray observatory. With 216 hr of observations of four dwarf spheroidal galaxies, we perform an unbinned likelihood analysis. We find no evidence of a γ-ray signal from UHDM annihilation above the background fluctuation for any individual dwarf galaxy nor for a joint-fit analysis, and consequently constrain the velocity-weighted annihilation cross section of UHDM for dark matter particle masses between 1 TeV and 30 PeV. We additionally set constraints on the allowed radius of a composite UHDM particle.Item Enhancing the speed of DNA walkers through soft confinement(Springer Nature, 2025-03-19) Ogieva, Mathew O.; Pfeifer, Wolfgang G.; Sensale, Sebastian; Physics, School of ScienceOver the past two decades, dynamic DNA origami structures have emerged as promising candidates for nanoscale signal and cargo transport. DNA walkers, programmable nanostructures that traverse tracks made of DNA, represent a key innovation in this field, enabling controlled and directional movement at the nanoscale. Despite relatively fast diffusion rates, the speed of DNA walkers remains constrained by the reaction-limited nature of strand exchange mechanisms, which depend both on the foothold-walker affinity and on the probability of the molecules being found close enough to bind. In this study, we explore how spatial confinement can expedite walker motion and evaluate two strategies to achieve this: the introduction of tailed DNA footholds, promoting pseudo-rotational dynamics, and the addition of walls along the DNA track, promoting pseudo-curvilinear dynamics. Using simulations and stochastic theories, we demonstrate that, by reducing the sampling of conformations far from the binding sites, tailed footholds provide the best speed enhancement, achieving a fourfold increase in speed. Trench-like confinement yields a more modest threefold increase, what, while significant, requires extensive structural modifications to the DNA track, limiting design flexibility and reducing cost-efficiency in comparison to the tailed footholds. The combination of tailed footholds and trench-like confinement turns the walker-foothold system bistable, with two distinct stable states separated by an energy barrier. By focusing on the properties of the DNA track, this study offers novel insights into leveraging soft structural motifs to optimize signal propagation rates, with implications for sensing, robotics and molecular computing in reaction-diffusion systems.